1. Field of the Invention
The present invention relates to a substrate holding rotating mechanism having plural spindles that hold and rotate a substrate, and also relates to a substrate processing apparatus having such a substrate holding rotating mechanism.
2. Description of the Related Art
As disclosed in Japanese laid-open patent publication No. 10-180198, there has been known a substrate holding rotating mechanism for use in cleaning or polishing a substrate, such as a semiconductor wafer. FIGS. 1A and 1B are schematic views each showing this kind of substrate holding rotating mechanism as viewed from above. As shown in FIG. 1A, this substrate holding rotating mechanism includes spindle groups 102 and 102, each comprising plural (two in the drawing) spindles 101, on both sides of a substrate W. The spindle groups 102 and 102 are provided respectively on plate-shaped base members 100 and 100, which are mounted on moving mechanisms (not shown in the drawings) that cause the base members 100 and 100 to move between substrate holding positions and waiting positions. The substrate holding rotating mechanism is operable to move the spindle groups 102 and 102 from the waiting positions to the substrate holding positions so as to bring clamp rollers 101a, provided on the respective spindles 101, into contact with a periphery of the substrate W to thereby hold (clamp) the substrate W. While holding the substrate W, the clamp rollers 101a are rotated to thereby rotate the substrate W.
This substrate holding rotating mechanism is designed such that, when holding the substrate W, the spindles 101 are positioned on the same circle as viewed from above, so that the clamp rollers 101a on the spindles 101 can press the periphery of the substrate W with equal pressures. However, the spindles 101 may be slightly off from the same circle due to deviation of the base members 100 from proper installation sites thereof, backlash of the moving mechanisms, or other causes. As a result, only one of the spindles 101 and 101 may come into contact with the substrate W, as shown in FIG. 1B, or even if both the spindles 101 come into contact with the substrate W, holding pressures thereof are not equal to one another. In other words, the clamp rollers 101a on the spindles 101 cannot apply equal holding pressures to the substrate W. Such unequal holding pressures would cause unstable rotation of the substrate W held by the clamp rollers 101a, resulting in a lowered efficiency of processing, such as cleaning, of the substrate W. Further, processing of many substrates with unequal holding pressures would cause a difference in wear of the clamp rollers 101a. As a result, replacement of the clamp rollers 101a is required prior to progression of wear, incurring an increased component cost and causing a lowered operating rate of the apparatus due to frequent maintenance.